1. The teacher starts by explaining the concept of volume as the amount of space occupied by a 3D object. 2. Using 45 identical cubes, the teacher constructs a cuboid with a square base, arranging the cubes in layers. 3. The teacher counts the number of cubes along one side of the square base, say $s$, and the number of cubes stacked vertically, the height $h$. 4. The teacher calculates the area of the square base as $s \times s = s^2$. 5. The teacher then counts the total number of cubes used, which is the volume $V$ of the cuboid. 6. The teacher shows that the total number of cubes $V$ equals the area of the base multiplied by the height, i.e., $$V = s^2 \times h$$. 7. This practical demonstration helps learners understand that the volume of a cuboid with a square base is the area of the base times the height, measured in cubic units.